A technique for detecting a gaze of a driver of a vehicle in order to assist the driver's driving is known. For example, there is a technique for detecting a gaze of a driver who is driving a vehicle, and for determining whether or not the driver is inattentive in driving (i.e., inattentive driving). When it is determined that the driver's driving is inattentive driving, a warning sound is outputted (see Patent Document 1 for example).
In order to detect the gaze, it is necessary to perform calibration for minimizing a gap between a detected direction of gaze and an actual direction of gaze. This calibration may be performed upon satisfaction of a predetermined condition. For example, when a location of the driver gazing object is identified, a gaze detection method is corrected, so that the driver gazing object lies in the detected direction of gaze (for example, see Patent Documents 2 and 3). For example, when a driver manipulates an operation switch in a vehicle compartment, it can be determined that the driver's eye is fixed to this operation switch.
When a driver conducts an operation to start the calibration, an image for gaze is displayed at a predetermined place and a gaze detection method is corrected, so that the gaze image lies in the detected direction of gaze (see Patent Document 4 for example).    Patent Document 1: JP-2010-39933A1    Patent Document 2: JP-H9-238905A1    Patent Document 3: JP-2009-15533A1    Patent Document 4: JP-H7-35543A1
According to the technique described in Patent Documents 2 and 3, the calibration can be performed while the driver is being unaware of whether or not the calibration is being performed. However, in this case, the driver cannot determine whether or not the calibration has been performed. Additionally, the driver cannot recognize accuracy of a current gaze detection result. Thus, the driver cannot determine whether or not a result of detection of the gaze detection apparatus is normal. The driver may have a feeling of anxiety, a feeling of discomfort, and a feeling of distrust toward a result of detection by a gaze detection apparatus.
For example, when a driver of a vehicle equipped with a gaze detection apparatus is changed into a new driver, a warning sound for the inattentive driving may be frequently outputted although the new driver looks in a front direction. In this case, the new driver cannot determine whether a cause of the frequent output of the warning sound is lack of calibration corresponding to the new driver or malfunction of the gaze detection apparatus. As a result, the driver may have the above-described feeling of anxiety and the like.
According to the technique described in Patent Document 4, although the driver can be aware of whether or not calibration has been performed, the driver can not recognize accuracy of a current gaze detection result.
Accordingly, the driver may have the above-described feeling of anxiety and the like.